1. Field of the Invention
This invention relates to concrete having improved compressive strength.
2. Description of the Prior Art
Concrete is a hard, strong building material made by mixing cement, sand, gravel and water. Water in the mixture causes the cement to set and bind the entire mixture in a hard mass. It is well known in concrete technology that the strength--usually the compressive strength as measured by the ASTM test C39-72--is a reliable criterion of general quality. For this reason, the whole technology of concrete is developed around obtaining a significant and practical strength with a minimum of cost, and a maximum of convenience in use. Despite extensive research, most of the concrete presently being used are simple mixtures of sand and coarse stone containing a minor proportion of portland cement with sufficient water being added to produce a mixture fluid enough to place in forms.
It is well known in the art that, the less water used in concrete, the higher the strength; considerable research has been directed to discovering mixtures of different particle sizes of sand and stone which will give fluid concrete having minimum water content. Various organic and inorganic additives have been found, which permit reduction in the water content of concrete. One such additive, Lomar.RTM. D, the sodium salt of naphthalene sulfonate formaldehyde condensate is used commercially for this purpose.
U.S. Pat. No. 3,537,869--Proell, issued Nov. 3, 1970 describes use of additives containing sulfonated condensation products of formaldehyde and naphthalene or salts thereof in concrete mixes to increase compressive strength of the hardened concrete.
U.S. Pat. No. 3,429,724--Keenum, Jr. et al, issued Feb. 25, 1969 describes use of zinc salts such as zinc chloride, zinc sulfate, zinc nitrate and zinc acetate to retard hardening of concrete mixes.